Pentode tube



Aug. 12, 1952 G. LEHMANN PENTODE TUBE Filed Sept. 8, 1947 4 INVENTOR GERARD LEHMANN BY A ORNEY Patented Aug. 12, 1952v I iEFPE E- PTQ GerardLehmann, Paris,jErance, -assignor to Intern'a tioiiaTS'taIndard Electric Corporatiom'hlew York} N.- Y;,' amorporati'on of Delaware I. .a s i t fiif and; this, permits L elimination ofv neutrodyning ,1circuits,=, except for very high irequencies.

rrhe difii u t e encountered ilibafiQn l i n.

ostetrpde vtub s e.-ma n y 9ua i l SQ iQ i Q lectrensg.emittedby the anode; Iti cordingly iprior knowledastq cm a m s -te rode calledfi n lfii qtgnq he gates-afield tential. an d ia; constant d ot that ofithqcathode'.flThls I athodegareiyeryl,freguently. .connected to theri: An. arrangement of. this has flnunrous drawba 'ks,'lparticularly in the case of tubes with circular gridseals.

: One of the obiects ofthe present 1 v iee on ry anbdelie e trp s' g Anqther'obj ect o f thepreserifi a ,9 ar nt tu ei alfi li i u I 91 c cu ar r d e es the sq gesso is; the en ealterat n s alan 'i d at a swam; manna. emcee. e ,v According to another feature of the present in vention, meansflare provided for incorporating the screen grid 'in a'olosed metallic surface that forms the anode cavity resonator.

According to another feature of the present in w vention, there is provided a screen g'rid whose outlet connection is disposed in such a wai v as to permitits incorporation in a, cl.osed surface thatiorms the anode cm rity,resonator The outlet connection of the suppressor grid is sulating bulb, secured to the intermediate bulb,

n .e ii ime to a.

; so 1 ccolr i s 12 1 v m ure q ii antgssetima Z a tic at d w h a q ss ed ciav tr 9 in such a way as not to destroy thec ady ntages cture.

Septeinber s sm, Serial N 12,751

secede L PubIic Law-690,.August 8,1946

-\.:Batehtj xpires August 20,1966

Qt-5 1st 15 w impedap aleiwe F 2, repr s s .7

ac ewith n Qth o e s.f eet fe ia aiadram e s of. the times e inventi n ll 'lt b d i ifre dl he following descriptiqngiir A hgrei i to 9; ythga pendeg. drawing m fi' tation and in which? r vi iz h r a Q eltett etv 2 i a s hema ic c a 91 dd (W 3 illustrates hematical nlexample of w w Psi-stu saimlq tures of the invention, rswF g' 5149 11 p qifimbq im n of a e to vt a if. PX. r a c r ct at corporates features of he present 'nv tion.

LF 5 is an w.- as sti fi Qt; thess arim of e bodim nt o iF s- According to modernconceptions} 0 f .va tubes; and since. the ado t'on-of, circ seals, the space between -two ele al 7. grid is 0 entirely distinct from the cat; associated with other spacesof the The possibility of incorporating the screen i r G o a t t o e. n sme a 'fi i i at-com let y .enq o e sths l caisson re ,in lylm e it os i e. to ram s .r-ag e ras lin s t ate st'w thm e t ,.c,.betw n t e, o fi m/g id Gstanqyihe A, sand to eliminate the neut osiy ina oil thea iibii- 45..lfi,er,; as. shown "in,- Fig. 1. c1o sed pa rity .4.vr sonatorsmayalsobeadapted to P t i tub If the. suppresson r d' G3 ofa neniode isis o vnecteditotheifcathode C, it-isnecessary topierce an opening throughinthejwall jthati ;.s, urrD11nds 50511118 anode; and extendsvthe:sbrenigrid Gij, as .1. shown in Figf2.

ii The existence of the orifice O: and 'of theficonnection between suppressor grid G3 and cathode C cancels the advantage of the arrangement ob- 55 tained by incorporating screen grid G2 in a.

3 closed surface surrounding anode A, and this constitutes a serious drawback in known arrangements.

The Linter-circuit coupling that results from the connection between cathode C and suppressor grid G3, and from orifice O, is so extensive that the circular seals for screen grid G2 become useless.

Another drawback of this arrangement is the connecting of grid G3 to the high frequency potential of cathode C. As a matter of fact; grid G3 is located at a slight distance from the anode. The capacitance G3-A is accordingly high, and

this capacitance is one of the well known drawbacks of pentode tubes.

Then again, the purpose of grid G3 is to prevent the secondary electrons from leaving the anode. To do this, the difference of potential created between grid G3 and anode A by the circuit has to be such that the field at the surface of the anode is constantly negative. The electrons that exist between A and G3 arethen impelled toward the anode, from which the secondary electrons cannot escape.

The present invention proposes to maintain a constant and low difi'erence of potential between anode A and suppressor grid G3, grid G3 being negative with respect to the anode.

For this purpose, the invention proposes to connect grid G3 to the alternating voltage of the anode and not of the cathode, theconstant potential of this grid being slightly lower than that of the anode.

Referring to Fig. 3 which illustrates schematically an example of embodiment incorporating features of the present invention, GI is the control electrode, G2 is the screen grid brought to a high potential with respect to the cathode, and Gi is the suppressor grid brought by means of a source P to a low and constant negative potential with respect to the anode.

Since the potential of G3 is stationary with respect to that of the anode, it is no longer necessary to-pierce an orifice through the surface S that forms the screening between the input and output circuits of the tube.

The only parasitic coupling that remains is that due to the interpenetration of the fields through the meshes of screen grid G2.

The oscillating output voltage is applied between screen grid G2 and the assembled suppressor grid GS-anode A.

Since the distance G2-G3 is great, the output capacitance is low.

Referring to Fig. 4, this illustrates an example of embodiment of a pentode tube of cylindrical structure that incorporates features of the present invention.

The tube is constructed around anode A, which is a cylinder, e. g. of copper, open at both ends.

For high powers, anode A carries cooling ribs 7 AR and it may even be provided with a cooling jacket having fluid circulation. One end of the anode cylinder carries an intermediate insulating bulb B2 traversed by a circular seal carryin screen grid G2 having its outlet at SGZ. To this intermediate bulb B2 there is secured an insulating bulb Bl traversed by the outlets SF of fllament F and the outlet SGI of control grid GI An insulating bulb B3 is secured to the other end of the anode cylinder and is traversed by the connection SG3 of the suppressor grid G3.

stant voltage, less than that of the anode, by a conductor which may, for example, pass within the copper tube that constitutes the anode inductance. Numerous known arrangements may be employed for reducing the grid G2-anode A alternating voltage.

At very high frequencies, the tube is associatedwith'coaxial circuits. In this case, the grid G3-anode A circuit may, for example, consist of a coaxial line element having a zero im pedance between G3 and A within the tube.

Although the present invention has been described in connection with an example ofa preferred embodiment, it is evident that it is by no means limited thereto, and that it is capable of numerous variants and modifications without departing from the scope of the invention.

What is claimed is:

1. A pentode tube of cylindrical structure comprising a cathode, a control grid, a screen grid, a suppressor grid, and an anode, all of cylindrical shape and mounted concentrically in the order named, an annular lead-out connection for said screen grid, a lead-out conductor connected to said suppressor grid, said lead-out conductor comprising a cylindrical tube coaxially disposed within said anode for inductive coupling therewith, the impedance to alternating current between said cylindrical tube and said anode being substantially zero at the operating frequency, and a metal tube directly connected to said anode and forming an inductive load therefor, said cylindrical tube forming said suppressor grid lead-out connection being located inside said metal tube and forming therewith a coaxial transmission line of low impedance.

2. A tube according to claim 1, in which said cylindrical anode is open at both ends, a metal annulus carrying said screen grid, an interme diate insulating bulb is connected between one end of said anode and said metal annulus, an end insulating bulb is supported on said annulus, output terminals from said cathode and control grid are sealed through said end bulb, and another end bulb is supported on the other end of said anode, said suppressor grid lead-out conductor being sealed therethrough.

GERARD LEHMANN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Llewellyn Aug. 19. 1947 

